Triacetonitrile(1,4,7-trimethyl-1,4,7-triazacyclononane)cobalt(II) bis(tetraphenylborate)

The title complex exhibits a distorted octahedral geometry about the cobalt centre. The divalent cobalt ion is surrounded by three acetonitrile solvento ligands and one tridentate tacn ligand.


Structure description
Cobalt complexes have attracted much attention due to their applications as catalysts for hydrogenation and hydrogen evolution reactions (Lin et al., 2017;Zhang et al., 2013Zhang et al., , 2017)).A rational design of catalyst is essential for the development of efficient cobalt catalysts.A scorpionate ligand allowing the facial coordination to a metal ion leads to the high-spin electronic configuration in low-coordinate cobalt complexes (Detrich et al., 1996;Cordeiro et al., 2021;Gu et al., 2023).Particularly, such a high-spin state of a monovalent cobalt ion allows the oxidative addition of dihydrogen, generating the cobalt dihydride, which is an important intermediate for the aforementioned catalyses.The 1,4,7-trimethyl-1,4,7-triazacyclononane (tacn) ligand exhibits an almost identical coordination mode with scorpionate ligands and it is proposed that a metal complex supported by tacn can display similar chemical and catalytic properties.Although tacn has also been introduced to cobalt, most of the resulting complexes show binuclear geometry.This study shows that [(tacn)Co(NCMe) 3 ][BPh 4 ] 2 is monomeric.
The single-crystal X-ray diffraction data reveals that the divalent cobalt ion adopts an octahedral geometry with six nitrogen donors of tacn and three acetonitrile ligands with two non-coordinating BPh 4 À ions (see Fig. 1).The tacn ligand is coordinated to the cobalt(II) center in the facial coordination fashion, exhibiting N tacn -Co1-N tacn bond angles of 83.16 (9), 82.86 (9) and 83.18 (9) � .The solvent ligands, acetonitrile, are also coordinated to cobalt in a cis manner.The three N tacn -Co1-N acetonitrile bond angles are 175.23 (9), 175.58 (9) and 176.62 (10) � , clearly showing the octahedral geometry of 1 (Table 1).The Co-N bond lengths ranging from 2.094 (3) to 2.153 (2) A ˚indicate that the high-spin divalent cobalt ion is supported by six l-type nitrogen donors (Kershaw Cook et al. 2013).This result corresponds to the 1 H NMR spectrum showing paramagnetic character.In the crystal, the discrete cobalt complexes and BPh 4 À anions are arranged along the b-axis direction (see Fig. 2).There are no directional intermolecular interactions or hydrogen bonding among molecular ions.
A search in the Cambridge Structural Database for structure 1 did not reveal any reported structures, including derivative searches.Similar dimeric cobalt compounds supported by tacn have been reported (Bossek et al. 1997;Thangavel et al. 2013) but a monomeric cobalt complex has not previously been structurally characterized.

Experimental details
Cobalt(II) bromide (CoBr 2 ), tacn, and sodium tetraphenylborate (NaBPh 4 ) were purchased from Sigma Aldrich.All manipulations were carried out using standard glovebox data reports Crystal Structure of 1 in a view along the crystallographic b-axis direction.
All hydrogen atoms are omitted for clarity.
techniques under N 2 atmosphere.Unless otherwise noted, solvents (THF and acetonitrile) were deoxygenated and dried by 4 A ˚molecular sieve.Tetrahydrofuran (THF) was tested with a standard purple solution of sodium benzophenone ketyl in THF in order to confirm effective oxygen and moisture removal.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.All H atoms were positioned with idealized geometry and refined isotropically with U iso (H) = 1.2U eq (C) using a riding model.

Figure 1 X
Figure 1X-ray crystal structure of 1 (ellipsoids at 50% probability).All hydrogen atoms are omitted for clarity.

Table 2
Experimental details.